Equipment for Tennis Pro

Hey everyone,
I just started teaching tennis,
and I need to get a tutor ball machine and I really dont know which is the best,
I'm not sure what kind, etc etc..
this is really scary because I really dont want to him a kid.. if you know what I mean
I found a couple of websites:http://www.sportstutor.com/tennis/tutor/
and this onehttp://www.twenga.com/price-tennis-t...l-machine.html
Please help me out, I really want to keep this job!
Thanks again!!
Have a great day